Where will we find the first telltale signs of the Anthropocene?

Dateline, January 1950. Isaac Asimov publishes Pebble in the Sky, his first science-fiction novel. George Orwell dies. And Earth enters a brand new epoch – according to some geologists.

Now the idea of the Anthropocene – the period in which human activity profoundly shapes the environment – has taken an important step closer to general acceptance. A working group of scientists has been mulling over the subject for seven years. This week 30 of its 35 members recommended adding the Anthropocene to our standard geological timescale.

The ultimate decision rests with the International Commission on Stratigraphy. If the ICS does accept the recommendation, the real work will begin. Somewhere near the top of the to-do list is one burning question: where in the world gives us the best view of the dawn of the Anthropocene?

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For every boundary between two geological periods, epochs or ages there is – or eventually will be – a Global Boundary Stratotype Section and Point (GSSP), sometimes called a golden spike. It’s the place that researchers have settled on as providing the best snapshot of our world lurching from one named chunk of geological time into the next.

“The most poignant place to mark the dawn of the Anthropocene would be on a coral reef”

If you want the best view of the dinosaur-filled Cretaceous giving way to the Palaeocene, for instance, the official advice is to go to El Kef in Tunisia. For the moment when the largest mass extinction in history eased us from the Permian period into the Triassic, head to Zhejiang Province in China.

So where might geologists one day single out as best marking the beginning of the Anthropocene?

“I suspect we will cast our net wide at the beginning,” says Jan Zalasiewicz at the University of Leicester, UK, who is convenor of the ICS’s Anthropocene Working Group. “There are lots of potential environments out there – lakes, anoxic [marine] basins, ice strata.”

The fact that the suggested shift into the Anthropocene is so recent might make the decision harder. Ideally the golden spike will be a site where something – like ice or sediment – is accumulating steadily enough to give us a recognisable year-by-year record. It also must be a place where this record isn’t in danger of being destroyed by either natural erosion or human activity.

This means one early suggestion – to define the Anthropocene’s golden spike as the regions of northern Europe where the area covered in human-worked soils has grown dramatically over the last few thousand years – might find few takers. We are still using and modifying those soils today, changing their identity each year.

And there’s another consideration: how best to define the dawn of the Anthropocene. Geological boundaries are usually tied to some sort of global event rather than a raw date. Such an event, marking the end of the Cretaceous, was when an asteroid impact showered a wide area with extraterrestrial iridium dust and triggered extinctions on land and in the sea.

It’s possible that many signals will have their role to play. “The Holocene is a good model,” says Zalasiewicz. The Holocene preceded the proposed Anthropocene, and its golden spike is an ice core from the Greenland ice sheet – one that preserves an isotopic signature of global warming at the end of the last ice age. Auxiliary sites around the world also exist, including a sediment core from a lake in Japan, which captures pollen changes associated with the rise in global temperature.

But that still leaves us with our initial question. Selecting sites that highlight different aspects of the Anthropocene doesn’t give us a definitive golden spike. So where in the world would it be?

Colin Waters at the British Geological Survey, another member of the Anthropocene Working Group, thinks that the Santa Barbara basin off the coast of California, and the Cariaco basin off Venezuela, are worth considering. Both accumulate sediment at a nice, steady rate, and that sediment – which might, for instance, contain a record of plutonium – isn’t likely to be disturbed by human activity or other processes.

We are all too familiar with the threats that coral reefs face as a consequence of global warming and ocean acidification. There would be something poetic in choosing a coral – plucked from somewhere like the Caribbean, according to Waters, to be stored in a museum – as the one object on Earth that best records the moment our planet entered its current period of intense human activity.